It is generally known that the pattern noise resulting from the tread pattern formed on the tread surface of a pneumatic tire can be reduced by somehow devising the pitch arrangement of the tread pattern. It is known also that the pattern noise can be reduced particularly by achieving a certain specific cycle arrangement or a random arrangement by employing three or more kinds of pitches (pitch lengths).
Recently, simulation has been carried out to evaluate in advance whether or not the pattern noise can be reduced, when a tread pattern having a new pitch arrangement is designed.
A pitch variation method is one of the well known noise simulation methods for evaluating the noise by simulation.
This pitch variation method comprises the steps of determining an amplitude waveform of the noise resulting from the tread pattern of one circumference of the tire from each data of a pitch arrangement, transforming the amplitude waveform to a Fourier series not having limitation to the pitch arrangement method, avoiding those spectrum waveforms in which the amplitude of a specific frequency exhibits an excessive peak among the spectrum waveforms, regarding the spectrum waveforms which are dispersed into a large number of sideband waves having lower levels, as superior, and evaluating them as a pitch arrangement having a low pattern noise.
However, when the pneumatic tires which are evaluated as having a low noise pattern by the evaluation method described above are fitted actually to a car and a feeling test of the pattern noise is carried out by a driver, the evaluation often results in that the tires do not have a low pattern noise.
Though various other evaluation methods have been studied so far, a pitch arrangement evaluation method whose simulation result always coincides with the actual car test has not yet been developed, and a satisfactory simulation evaluation method has been desired earnestly.
It is therefore an object of the present invention to provide an evaluation method of a tread pattern pitch arrangement of a pneumatic tire which can always bring the simulation evaluation result of a low pattern noise resulting from the pitch arrangement into conformity with the actual measurement result.